The invention relates to monitoring the performance of a brake, specifically a brake which is biased to its operational or braking position.
For safety reasons, machinery which requires to be braked is frequently fitted with brakes which are biased to be operative, that is, to apply a braking effect to the machinery, so that this can operate only by the application to the brake of a controllable force opposing the bias. Typically such a brake device will be actuated by a compression spring or springs, the device being held inoperative to allow operation of the machinery in which it is incorporated by application, pneumatically, hydraulically or electrically, of a disengaging or balance force.
In such a brake device, the braking force available from the springs may reduce with time for various reasons. For example, wear in friction components in the brake device can cause the compressed length of the springs to increase. Also, one (or more) of the springs might lose some or all of its force through gradual softening, or fail through actual fracture or through rapid softening.
The result of any reduction in the spring force would be a reduction in the braking effect. If this reduction is gradual, as would occur because of friction component wear or gradual softening of the springs, the reduced braking force may well be detected because the machinery takes longer to stop or because of a change in the position to which the machinery comes to rest, as in the case of a mechanical press or shear which is desirably brought to rest at a predetermined position, typically top dead centre. Such effects should be noted during normal maintenance and the brake overhauled accordingly.
However, if the reduction in the spring braking force is more rapid, as because of component failure, or rapid softening of the springs, the resulting reduction in brake performance may not be seen until a failure to stop the machinery occurs. The consequences of such a brake failure could be serious, and could include injury to persons, particularly when the brake device is intended to stop the machinery in the event of an emergency.